The relationship between 3',5'-cyclic adenosine monophosphate and calcium in mediating follicle-stimulating hormone signal transduction in Sertoli cells.

Abstract

FSH signal transduction in Sertoli cells involves the generation of cAMP and calcium as second messengers; however, the relationship between these two signals is not clear. In order to determine whether these were serial or parallel signals, we studied cytosolic calcium levels in freshly isolated rat Sertoli cells using maneuvers to dissociate generation of endogenous cAMP from cytosolic calcium. Pretreatment with 1 mM MDL 12,330A, an adenylate cyclase inhibitor, reduced by greater than 90% increases in cytosolic calcium induced by FSH (97 +/- 6 vs. 213 +/- 16 nM), whereas, despite adenylate cyclase blockade, 1 mM (Bu)2cAMP continued to elevate cytosolic calcium (from 87 +/- 6 to 182 +/- 23 nM), indicating the involvement of adenylate cyclase in the FSH-induced rise of cytosolic calcium. A cAMP antagonist, 1 mM Rp-cAMP, reduced by 75% the FSH-induced rise of cytosolic calcium (115 +/- 14 vs. 213 +/- 16 nM), suggesting that endogenous cAMP levels generated by FSH are sufficient to activate the cytosolic calcium response to FSH. Pretreatment with pertussis toxin (1 mg/liter) to dissociate the FSH-receptor interaction from its G-protein-mediated linkage to adenylate cyclase also suppressed the FSH-induced rise in cytosolic calcium (97 +/- 11 vs. 213 +/- 16 nM). Sertoli cells preincubated with 1 mM staurosporine, an inhibitor of protein kinases, exhibited a reduced calcium response to FSH (125 +/- 14 vs. 213 +/- 16 nM), suggesting that FSH-induced calcium flux might be mediated by protein kinase, presumably cAMP-dependent protein kinase A. The present findings therefore strengthen the premise that the cytosolic calcium response to FSH in Sertoli cells is predominantly attributable to serial signaling after the generation of endogenous cAMP.